1. Field of Invention
The present invention relates to a hydrogel microparticle composition. More particularly, the present invention relates to a composite hydrogel microparticle composition containing chitosan.
2. Description of Related Art
Hydrogels have been applied widely in biomedical fields, such as wound dressings, haemostatic materials, controlled drug release system and so on. Moreover, hydrogel can be used as artificial intraocular lens and implants for plastic surgery. In the recent development, composite hydrogels with additional function(s) have been given more and more attention. Such composite hydrogels can be applied in the fields of artificial skins, wound dressings, cell and tissue cultures, face masks and the like.
In U.S. Pat. No. 6,486,213, Chen et al. disclose block and graft copolymers, and hydrogels thereof, which contain both a temperature-sensitive polymer component and a pH-sensitive polymer component. Such copolymers can be used for topical drug delivery to a treatment area. According to the method and example described in Chen et al., the resulting grafted copolymer is a disk-like or sheet-like hydrogel.
Kubota, in U.S. Pat. No. 5,834,007, discloses a polymer, which has a sol-gel transition temperature in an aqueous solution. The polymer has a substantial water-insolubility at a temperature higher than the sol-gel transition temperature, thereby existing in a gel-state. The polymer has a reversible water-solubility at a temperature lower than the sol-gel transition temperature, thereby existing in a sol-state.
In U.S. Pat. No. 5,420,197, Lorenz et al. disclose a dermatologically-compatible composition comprising a hydrophilic gel which comprises a blend of a neutralized chitosan and a hydrophilic poly (N-vinyl lactam). The product is used in, for example, wound dressings, burn dressings, drug delivery dressings, cosmetic mask dressings, and the like.
A highly absorbent modified polysaccharide is taught by Reid et al. in U.S. Pat. No. 4,028,290. According to Reid et al., the modified polysaccharides are prepared by reacting a polysaccharide such as cellulose or starch in the presence of acrylamide, another vinyl monomer and a divinyl crosslinking monomer using free radical polymerization techniques. The product is a complex mixture of crosslinked grafted polysaccharide and acrylamide copolymers. Reid et al. also teach that product is water soluble, and hence, it is desirable to keep the amount of the water relatively low with respect to the reactants so that a relatively high vinyl monomer concentration will be maintained in the vicinities of the polysaccharide particles. To this end, only enough water is used to dissolve the monomers and uniformly wet the polysaccharide, about 1.5 to 2.5 parts per part of reactants. Moreover, according to Reid et al., an inert water-immiscible diluent, such as toluene, is employed as the reaction medium; otherwise, the yields of the products are substantially lowered.
Omidian et al., in U.S. Pat. No. 6,960,617, disclose porous or superporous hydrogels having improved elasticity and mechanical strength properties. The porous or superporous hydrogels are obtained by subjecting a hydrogel formulation containing a strengthening agent to chemical or physical crosslinking conditions subsequent to initial gel formation. According to Omidian et al., it is important to control the monomer concentration (dilution with water) and comonomer (acrylic acid) concentration so as to achieve a desirable gelation property that results in the porous or superporous hydrogels.
The above-identified documents teach hydrogels in the form of bulk materials, and neither of them discloses hydrogel particles and methods for preparing the same.
Bozigian et al., on the other hand, disclose a method for preparing hydrogel particles in U.S. Pat. No. 5,977,428. According to Bozigian et al., polyacrylonitrile (PAN) is formed as a solid aquagel, and the PAN aquagel is subjected to a base hydrolysis and then dried to obtain the hydrogel particles.
Conventionally, the hydrogel particles are prepared in a two-stage manner, such as the method described in Bozigian et al. Specifically, the bulk hydrogel material is first formed in the formed of a block polymer (or copolymer, grafted polymer), and then the hydrogel is processed (dried or granulized) to produce hydrogel particles.
In view of the forgoing, there exists a need in the related art to provide a method for preparing hydrogel microparticles of substantially uniform particle sizes.